An axial flow, gas turbine engine typically has a compression section, a combustion section and a turbine section. An annular flowpath for working medium gases extends axially through the sections of the engine. A stator assembly extends inwardly and outwardly of and about the annular flowpath for confining the working medium gases to the flowpath and for directing the working medium gases along the flowpath.
As the gases are passed along the flowpath, the gases are pressurized in the compression section and burned with fuel in the combustion section to add energy to the gases. The hot, pressurized gases are expanded in the turbine section to produce useful work. A major portion of this work is used as output power, such as for driving a free turbine or developing thrust for aircraft.
A remaining portion of the work generated by the turbine section is not used for output power. Instead, this portion of the work is used in the compression section of the engine to pressurize the working medium gases for the combustion section and for providing cooling air to selected locations in the engine. A rotor assembly extends through the engine for transferring this work from the turbine section to the compression section. The rotor assembly has arrays of rotor blades in the compression section for doing work on the working medium gases and arrays of rotor blades in the turbine section for receiving work from the working medium gases. The rotor blades in the turbine section have airfoils that extend outwardly across the working medium flowpath. The turbine airfoils are angled to the approaching flow to receive the work from the gases and to drive the rotor assembly about the axis of rotation.
The stator assembly in both sections has an inner case and an outer case for bounding the working medium flowpath. Arrays of stator vanes extend across the working medium flowpath between the cases. The arrays of stator vanes are disposed in interdigitated fashion with the arrays of rotor blades. Each stator vane includes an outer wall segment or platform which bound the flow path, forming an array of outer wall segments. Each stator vane has one or more airfoils that extend inwardly from the outer platform. The airfoils direct the approaching flow to the adjacent row of rotor blades at the desired angle.
The stator assembly further includes a second array of wall segments which are disposed between the arrays of stator vanes and outwardly of the rotor blades. The second array of wall segments, commonly referred to as an outer air seal, are supported from the outer case and extend circumferentially about the working medium flowpath. The segments are circumferentially spaced leaving a clearance gap therebetween. The clearance gap is provided to accommodate changes in diameter of the array of wall segments in response to operative conditions of the engine as the outer case is heated and expands or is cooled and contracts.
The stator assembly includes a support structure, such as upstream support and a downstream support, for supporting the seal segments of the outer air seal from the outer case. The seal segments are adapted by flanges to engage the supports. These flanges are typically called “hooks.” The outer case and the support structure position the seal segments in close proximity to the blades and provide a seal surface which radially faces the working medium gases. The seal surface blocks the leakage of working medium gases past the tips of the rotor blades.
The inwardly facing surfaces of the seal segments are commonly formed with abradable material to enable the seal segments to accept rubbing contact with the tips of the rotor blades under operative conditions. As a result, the rotor blades exert a circumferential force and moment on the seal segments urging the seal segments in the circumferential direction about the axis of the engine. The forces and the moment are resisted by the support structure.
The outer air seal assembly typically includes pins that extend between one of the supports and the outer air seal segment to restrain the segments against the circumferentially directed forces. An example of such pins is shown in U.S. Pat. 4,247,248 issued to Chaplin, DeTolla and Griffin entitled “Outer Air Seal Support Structure For Gas Turbine Engine.” In addition to resisting the forces and moments arising from rubbing contact between the rotor blades and the surface of the outer air seal segment, these pins locate the outer air seal segments. These pins require the machining of appropriate openings to receive the pins, require installation in a location that is difficult to reach and to inspect, and, require the manufacture and maintenance of additional parts for the engine.
As a result of being disposed adjacent to the flowpath, the surfaces of the segments and the segments themselves are in intimate contact with the hot working medium gases. The segments receive heat from the gases and the segments are cooled to keep the temperature of the segments within acceptable limits. Pressurized cooling air is flowed from supply chambers on the interior of the outer air seal assembly through cooling air holes to the exterior surface of the segments. The cooling air provides transpiration cooling as the air passes through walls of the seal segments and, after the air is discharged from the segments, provides film cooling with a film of air on the exterior of the segments. The film of cooling air provides a barrier between the segments and the hot, working medium gases.
Leak paths exist from the supply chambers of cooling air to the working medium flowpath because of the segmented nature of the outer air seal segments and the supports. These leak paths divert cooling air away from locations where the cooling air provides helpful cooling. These leak paths decrease the aerodynamic efficiency of the engine because the engine expended work to compress the cooling air. Any reduction in cooling air consumption reduces the performance penalty caused by the work of pressurization. As a result, seal chambers are provided to intercept the leak paths at critical locations in the engine to decrease the loss of cooling air.
One example of such a seal chamber in another part of the turbine section is shown in U.S. Pat. No. 4,336,943 issued to Chaplin entitled “Wedge-Shaped Seal for Flanged Joints.” In Chaplin, the seal chamber is provided with a seal member or ring. The ring has arms which open toward a region of higher pressure. The arms are each urged against a surface bounding the seal chamber to block the loss of cooling air from the engine.
This type of seal member is also employed adjacent to outer air seal assemblies in conjunction with the support for the adjacent array of stator vanes. The vane support and the outer air seal assembly form the seal chamber for the seal member to locate, position, and retain the seal member. Inspection of the disposition of the seal member after installation requires disassembly of the adjacent vane support.
The above art notwithstanding, scientists and engineers working under the direction of Applicants' Assignee have sought to develop structure for blocking a leak path through a seal chamber that uses a resilient seal member disposed between two circumferentially extending structures bounding the flow path and which facilitates assembly, disassembly and inspection of the disposition of the resilient seal member and locating and retaining the resilient seal member under non-operative and operative conditions of the engine.